A module zsh/net/tcp is provided to provide network I/O over TCP/IP from
within the shell; see its description in zshmodules(1). This manual
page describes a function suite based on the module. If the module is
installed, the functions are usually installed at the same time, in which case
they will be available for autoloading in the default function search path. In
addition to the zsh/net/tcp module, the zsh/zselect module is
used to implement timeouts on read operations. For troubleshooting tips,
consult the corresponding advice for the zftp functions described in
zshzftpsys(1).

There are functions corresponding to the basic I/O operations
open, close, read and send, named tcp_open etc., as well as a
function tcp_expect for pattern match analysis of data read as input.
The system makes it easy to receive data from and send data to multiple
named sessions at once. In addition, it can be linked with the shell's line
editor in such a way that input data is automatically shown at the terminal.
Other facilities available including logging, filtering and configurable
output prompts.

To use the system where it is available, it should be enough to
`autoload -U tcp_open' and run tcp_open as documented below to
start a session. The tcp_open function will autoload the remaining
functions.

Open a new session. In the first and simplest form, open a TCP connection
to host host at port port; numeric and symbolic forms are
understood for both.

If sess is given, this becomes the name of the session
which can be used to refer to multiple different TCP connections. If
sess is not given, the function will invent a numeric name value
(note this is not the same as the file descriptor to which the
session is attached). It is recommended that session names not include
`funny' characters, where funny characters are not well-defined but
certainly do not include alphanumerics or underscores, and certainly do
include whitespace.

In the second case, one or more sessions to be opened are given by
name. A single session name is given after -s and a comma-separated
list after -l; both options may be repeated as many times as
necessary. A failure to open any session causes tcp_open to abort.
The host and port are read from the file .ztcp_sessions in the same
directory as the user's zsh initialisation files, i.e. usually the home
directory, but $ZDOTDIR if that is set. The file consists of lines
each giving a session name and the corresponding host and port, in that
order (note the session name comes first, not last), separated by
whitespace.

The third form allows passive and fake TCP connections. If the
option -a is used, its argument is a file descriptor open for
listening for connections. No function front-end is provided to open such a
file descriptor, but a call to `ztcp -lport' will create one
with the file descriptor stored in the parameter $REPLY. The
listening port can be closed with `ztcp -cfd'. A call to
`tcp_open -afd' will block until a remote TCP connection is
made to port on the local machine. At this point, a session is
created in the usual way and is largely indistinguishable from an active
connection created with one of the first two forms.

If the option -f is used, its argument is a file descriptor
which is used directly as if it were a TCP session. How well the remainder
of the TCP function system copes with this depends on what actually
underlies this file descriptor. A regular file is likely to be unusable; a
FIFO (pipe) of some sort will work better, but note that it is not a good
idea for two different sessions to attempt to read from the same FIFO at
once.

If the option -q is given with any of the three forms,
tcp_open will not print informational messages, although it will in
any case exit with an appropriate status.

If the line editor (zle) is in use, which is typically the case if
the shell is interactive, tcp_open installs a handler inside zle
which will check for new data at the same time as it checks for keyboard
input. This is convenient as the shell consumes no CPU time while waiting;
the test is performed by the operating system. Giving the option -z
to any of the forms of tcp_open prevents the handler from being
installed, so data must be read explicitly. Note, however, this is not
necessary for executing complete sets of send and read commands from a
function, as zle is not active at this point. Generally speaking, the
handler is only active when the shell is waiting for input at a command
prompt or in the vared builtin. The option has no effect if zle is
not active; `[[ -o zle]]' will test for this.

The first session to be opened becomes the current session and
subsequent calls to tcp_open do not change it. The current session is
stored in the parameter $TCP_SESS; see below for more detail about
the parameters used by the system.

The function tcp_on_open, if defined, is called when a
session is opened. See the description below.

tcp_close [ -qn ] [ -a | -lsess[,...] | sess ... ]

Close the named sessions, or the current session if none is given, or all
open sessions if -a is given. The options -l and -s
are both handled for consistency with tcp_open, although the latter
is redundant.

If the session being closed is the current one, $TCP_SESS
is unset, leaving no current session, even if there are other sessions still
open.

If the session was opened with tcp_open -f, the file
descriptor is closed so long as it is in the range 0 to 9 accessible
directly from the command line. If the option -n is given, no attempt
will be made to close file descriptors in this case. The -n option is
not used for genuine ztcp session; the file descriptors are always
closed with the session.

If the option -q is given, no informational messages will
be printed.

tcp_read [ -bdq ] [ -tTO ] [ -TTO ]

[ -a | -ufd[,...] | -lsess[,...] | -ssess ... ]

Perform a read operation on the current session, or on a list of sessions
if any are given with -u, -l or -s, or all open
sessions if the option -a is given. Any of the -u, -l
or -s options may be repeated or mixed together. The -u
option specifies a file descriptor directly (only those managed by this
system are useful), the other two specify sessions as described for
tcp_open above.

The function checks for new data available on all the sessions
listed. Unless the -b option is given, it will not block waiting for
new data. Any one line of data from any of the available sessions will be
read, stored in the parameter $TCP_LINE, and displayed to standard
output unless $TCP_SILENT contains a non-empty string. When printed
to standard output the string $TCP_PROMPT will be shown at the start
of the line; the default form for this includes the name of the session
being read. See below for more information on these parameters. In this
mode, tcp_read can be called repeatedly until it returns status 2
which indicates all pending input from all specified sessions has been
handled.

With the option -b, equivalent to an infinite timeout, the
function will block until a line is available to read from one of the
specified sessions. However, only a single line is returned.

The option -d indicates that all pending input should be
drained. In this case tcp_read may process multiple lines in the
manner given above; only the last is stored in $TCP_LINE, but the
complete set is stored in the array $tcp_lines. This is cleared at
the start of each call to tcp_read.

The options -t and -T specify a timeout in seconds,
which may be a floating point number for increased accuracy. With -t
the timeout is applied before each line read. With -T, the timeout
applies to the overall operation, possibly including multiple read
operations if the option -d is present; without this option, there is
no distinction between -t and -T.

The function does not print informational messages, but if the
option -q is given, no error message is printed for a non-existent
session.

A return status of 2 indicates a timeout or no data to read. Any
other non-zero return status indicates some error condition.

See tcp_log for how to control where data is sent by
tcp_read.

tcp_send [ -cnq ] [ -ssess | -lsess[,...] ] data ...

tcp_send [ -cnq ] -adata ...

Send the supplied data strings to all the specified sessions in turn. The
underlying operation differs little from a `print -r' to the
session's file descriptor, although it attempts to prevent the shell from
dying owing to a SIGPIPE caused by an attempt to write to a defunct
session.

The option -c causes tcp_send to behave like
cat. It reads lines from standard input until end of input and sends
them in turn to the specified session(s) exactly as if they were given as
data arguments to individual tcp_send commands.

The option -n prevents tcp_send from putting a
newline at the end of the data strings.

The remaining options all behave as for tcp_read.

The data arguments are not further processed once they have been
passed to tcp_send; they are simply passed down to print
-r.

If the parameter $TCP_OUTPUT is a non-empty string and
logging is enabled then the data sent to each session will be echoed to the
log file(s) with $TCP_OUTPUT in front where appropriate, much in the
manner of $TCP_PROMPT.

With an argument logfile, all future input from tcp_read
will be logged to the named file. Unless -a (append) is given, this
file will first be truncated or created empty. With no arguments, show the
current status of logging.

With the option -s, per-session logging is enabled. Input
from tcp_read is output to the file
logfile.sess. As the session is automatically
discriminated by the filename, the contents are raw (no $TCP_PROMPT).
The option -a applies as above. Per-session logging and logging of
all data in one file are not mutually exclusive.

The option -c closes all logging, both complete and
per-session logs.

The options -n and -N respectively turn off or
restore output of data read by tcp_read to standard output; hence
`tcp_log -cn' turns off all output by tcp_read.

The function is purely a convenient front end to setting the
parameters $TCP_LOG, $TCP_LOG_SESS, $TCP_SILENT, which
are described below.

tcp_renameoldnew

Rename session old to session new. The old name becomes
invalid.

tcp_sess [ sess [ command [ arg ... ] ] ]

With no arguments, list all the open sessions and associated file
descriptors. The current session is marked with a star. For use in
functions, direct access to the parameters $tcp_by_name,
$tcp_by_fd and $TCP_SESS is probably more convenient; see
below.

With a sess argument, set the current session to
sess. This is equivalent to changing $TCP_SESS directly.

With additional arguments, temporarily set the current session
while executing `commandarg ...'. command is
re-evaluated so as to expand aliases etc., but the remaining args are
passed through as that appear to tcp_sess. The original session is
restored when tcp_sess exits.

This is a convenient front-end to tcp_send. All arguments are
passed to tcp_send, then the function pauses waiting for data.
While data is arriving at least every $TCP_TIMEOUT (default 0.3)
seconds, data is handled and printed out according to the current
settings. Status 0 is always returned.

This is generally only useful for interactive use, to prevent the
display becoming fragmented by output returned from the connection. Within a
programme or function it is generally better to handle reading data by a
more explicit method.

tcp_expect [ -q ] [ -pvar | -Pvar ] [ -tTO | -TTO ]

[ -a | -ssess | -lsess[,...] ] pattern ...

Wait for input matching any of the given patterns from any of the
specified sessions. Input is ignored until an input line matches one of
the given patterns; at this point status zero is returned, the matching
line is stored in $TCP_LINE, and the full set of lines read during
the call to tcp_expect is stored in the array
$tcp_expect_lines.

Sessions are specified in the same way as tcp_read: the
default is to use the current session, otherwise the sessions specified by
-a, -s, or -l are used.

Each pattern is a standard zsh extended-globbing pattern;
note that it needs to be quoted to avoid it being expanded immediately by
filename generation. It must match the full line, so to match a substring
there must be a `*' at the start and end. The line matched against
includes the $TCP_PROMPT added by tcp_read. It is possible to
include the globbing flags `#b' or `#m' in the patterns to
make backreferences available in the parameters $MATCH,
$match, etc., as described in the base zsh documentation on pattern
matching.

Unlike tcp_read, the default behaviour of tcp_expect
is to block indefinitely until the required input is found. This can be
modified by specifying a timeout with -t or -T; these function
as in tcp_read, specifying a per-read or overall timeout,
respectively, in seconds, as an integer or floating-point number. As
tcp_read, the function returns status 2 if a timeout occurs.

The function returns as soon as any one of the patterns given
match. If the caller needs to know which of the patterns matched, the option
-pvar can be used; on return, $var is set to the
number of the pattern using ordinary zsh indexing, i.e. the first is 1, and
so on. Note the absence of a `$' in front of var. To avoid
clashes, the parameter cannot begin with `_expect'. The index -1 is
used if there is a timeout and 0 if there is no match.

The option -Pvar works similarly to -p, but
instead of numerical indexes the regular arguments must begin with a prefix
followed by a colon: that prefix is then used as a tag to which var
is set when the argument matches. The tag timeout is used if there is
a timeout and the empty string if there is no match. Note it is acceptable
for different arguments to start with the same prefix if the matches do not
need to be distinguished.

The option -q is passed directly down to
tcp_read.

As all input is done via tcp_read, all the usual rules
about output of lines read apply. One exception is that the parameter
$tcp_lines will only reflect the line actually matched by
tcp_expect; use $tcp_expect_lines for the full set of lines
read during the function call.

tcp_proxy

This is a simple-minded function to accept a TCP connection and execute a
command with I/O redirected to the connection. Extreme caution should be
taken as there is no security whatsoever and this can leave your computer
open to the world. Ideally, it should only be used behind a firewall.

The first argument is a TCP port on which the function will
listen.

The remaining arguments give a command and its arguments to
execute with standard input, standard output and standard error redirected
to the file descriptor on which the TCP session has been accepted. If no
command is given, a new zsh is started. This gives everyone on your network
direct access to your account, which in many cases will be a bad thing.

The command is run in the background, so tcp_proxy can then
accept new connections. It continues to accept new connections until
interrupted.

tcp_spam [ -ertv ] [ -a | -ssess |
-lsess[,...] ] cmd [ arg ... ]

Execute `cmd [ arg ... ]' for each session in turn. Note
this executes the command and arguments; it does not send the command line
as data unless the -t (transmit) option is given.

The sessions may be selected explicitly with the standard
-a, -s or -l options, or may be chosen implicitly. If
none of the three options is given the rules are: first, if the array
$tcp_spam_list is set, this is taken as the list of sessions,
otherwise all sessions are taken. Second, any sessions given in the array
$tcp_no_spam_list are removed from the list of sessions.

Normally, any sessions added by the `-a' flag or when all
sessions are chosen implicitly are spammed in alphabetic order; sessions
given by the $tcp_spam_list array or on the command line are spammed
in the order given. The -r flag reverses the order however it was
arrived it.

The -v flag specifies that a $TCP_PROMPT will be
output before each session. This is output after any modification to
TCP_SESS by the user-defined tcp_on_spam function described
below. (Obviously that function is able to generate its own output.)

If the option -e is present, the line given as `cmd
[ arg ... ]' is executed using eval, otherwise it is executed
without any further processing.

tcp_talk

This is a fairly simple-minded attempt to force input to the line editor
to go straight to the default TCP_SESS.

An escape string, $TCP_TALK_ESCAPE, default `:', is
used to allow access to normal shell operation. If it is on its own at the
start of the line, or followed only by whitespace, the line editor returns
to normal operation. Otherwise, the string and any following whitespace are
skipped and the remainder of the line executed as shell input without any
change of the line editor's operating mode.

The current implementation is somewhat deficient in terms of use
of the command history. For this reason, many users will prefer to use some
form of alternative approach for sending data easily to the current session.
One simple approach is to alias some special character (such as `%')
to `tcp_command --'.

tcp_wait

The sole argument is an integer or floating point number which gives the
seconds to delay. The shell will do nothing for that period except wait
for input on all TCP sessions by calling tcp_read -a. This is
similar to the interactive behaviour at the command prompt when zle
handlers are installed.

This pair of functions provide a simple way to transfer a file between two
hosts within the shell. Note, however, that bulk data transfer is
currently done using cat. tcp_point reads any data arriving
at port and sends it to standard output; tcp_shoot connects
to port on host and sends its standard input. Any unused
port may be used; the standard mechanism for picking a port is to
think of a random four-digit number above 1024 until one works.

To transfer a file from host woodcock to host
springes, on springes:

tcp_point 8091 >output_file

and on woodcock:

tcp_shoot springes 8091 <input_file

As these two functions do not require tcp_open to set up a
TCP connection first, they may need to be autoloaded separately.

Certain functions, if defined by the user, will be called by the function system
in certain contexts. This facility depends on the module zsh/parameter,
which is usually available in interactive shells as the completion system
depends on it. None of the functions need be defined; they simply provide
convenient hooks when necessary.

Typically, these are called after the requested action has been
taken, so that the various parameters will reflect the new state.

tcp_on_aliasaliasfd

When an alias is defined, this function will be called with two arguments:
the name of the alias, and the file descriptor of the corresponding
session.

tcp_on_awolsessfd

If the function tcp_fd_handler is handling input from the line
editor and detects that the file descriptor is no longer reusable, by
default it removes it from the list of file descriptors handled by this
method and prints a message. If the function tcp_on_awol is defined
it is called immediately before this point. It may return status 100,
which indicates that the normal handling should still be performed; any
other return status indicates that no further action should be taken and
the tcp_fd_handler should return immediately with the given status.
Typically the action of tcp_on_awol will be to close the
session.

The variable TCP_INVALIDATE_ZLE will be a non-empty string
if it is necessary to invalidate the line editor display using `zle
-I' before printing output from the function.

(`AWOL' is military jargon for `absent without leave' or some
variation. It has no pre-existing technical meaning known to the
author.)

tcp_on_closesessfd

This is called with the name of a session being closed and the file
descriptor which corresponded to that session. Both will be invalid by the
time the function is called.

tcp_on_opensessfd

This is called after a new session has been defined with the session name
and file descriptor as arguments. If it returns a non-zero status, opening
the session is assumed to fail and the session is closed again; however,
tcp_open will continue to attempt to open any remaining sessions
given on the command line.

tcp_on_renameoldsessfdnewsess

This is called after a session has been renamed with the three arguments
old session name, file descriptor, new session name.

tcp_on_spamsesscommand ...

This is called once for each session spammed, just before a command
is executed for a session by tcp_spam. The arguments are the
session name followed by the command list to be executed. If
tcp_spam was called with the option -t, the first command
will be tcp_send.

This function is called after $TCP_SESS is set to reflect
the session to be spammed, but before any use of it is made. Hence it is
possible to alter the value of $TCP_SESS within this function. For
example, the session arguments to tcp_spam could include extra
information to be stripped off and processed in tcp_on_spam.

If the function sets the parameter $REPLY to `done',
the command line is not executed; in addition, no prompt is printed for the
-v option to tcp_spam.

tcp_on_unaliasaliasfd

This is called with the name of an alias and the corresponding session's
file descriptor after an alias has been deleted.

The following functions are used by the TCP function system but will rarely if
ever need to be called directly.

tcp_fd_handler

This is the function installed by tcp_open for handling input from
within the line editor, if that is required. It is in the format
documented for the builtin `zle -F' in zshzle(1) .

While active, the function sets the parameter
TCP_HANDLER_ACTIVE to 1. This allows shell code called internally
(for example, by setting tcp_on_read) to tell if is being called when
the shell is otherwise idle at the editor prompt.

tcp_output [ -q ] -Pprompt-Ffd-Ssess

This function is used for both logging and handling output to standard
output, from within tcp_read and (if $TCP_OUTPUT is set)
tcp_send.

The prompt to use is specified by -P; the default is
the empty string. It can contain:

%c

Expands to 1 if the session is the current session, otherwise 0. Used with
ternary expressions such as `%(c.-.+)' to output `+' for the
current session and `-' otherwise.

%f

Replaced by the session's file descriptor.

%s

Replaced by the session name.

%%

Replaced by a single `%'.

The option -q suppresses output to standard output, but not
to any log files which are configured.

The -S and -F options are used to pass in the
session name and file descriptor for possible replacement in the prompt.

Parameters follow the usual convention that uppercase is used for scalars and
integers, while lowercase is used for normal and associative array. It is
always safe for user code to read these parameters. Some parameters may also
be set; these are noted explicitly. Others are included in this group as they
are set by the function system for the user's benefit, i.e. setting them is
typically not useful but is benign.

It is often also useful to make settable parameters local to a
function. For example, `local TCP_SILENT=1' specifies that data read
during the function call will not be printed to standard output, regardless
of the setting outside the function. Likewise, `local
TCP_SESS=sess' sets a session for the duration of a function, and
`localTCP_PROMPT=' specifies that no prompt is used for input
during the function.

tcp_expect_lines

Array. The set of lines read during the last call to tcp_expect,
including the last ($TCP_LINE).

tcp_filter

Array. May be set directly. A set of extended globbing patterns which, if
matched in tcp_output, will cause the line not to be printed to
standard output. The patterns should be defined as described for the
arguments to tcp_expect. Output of line to log files is not
affected.

TCP_HANDLER_ACTIVE

Scalar. Set to 1 within tcp_fd_handler to indicate to functions
called recursively that they have been called during an editor session.
Otherwise unset.

TCP_LINE

The last line read by tcp_read, and hence also
tcp_expect.

TCP_LINE_FD

The file descriptor from which $TCP_LINE was read.
${tcp_by_fd[$TCP_LINE_FD]} will give the corresponding session
name.

tcp_lines

Array. The set of lines read during the last call to tcp_read,
including the last ($TCP_LINE).

TCP_LOG

May be set directly, although it is also controlled by tcp_log. The
name of a file to which output from all sessions will be sent. The output
is proceeded by the usual $TCP_PROMPT. If it is not an absolute
path name, it will follow the user's current directory.

TCP_LOG_SESS

May be set directly, although it is also controlled by tcp_log. The
prefix for a set of files to which output from each session separately
will be sent; the full filename is ${TCP_LOG_SESS}.sess.
Output to each file is raw; no prompt is added. If it is not an absolute
path name, it will follow the user's current directory.

tcp_no_spam_list

Array. May be set directly. See tcp_spam for how this is used.

TCP_OUTPUT

May be set directly. If a non-empty string, any data sent to a session by
tcp_send will be logged. This parameter gives the prompt to be used
in a file specified by $TCP_LOG but not in a file generated from
$TCP_LOG_SESS. The prompt string has the same format as
TCP_PROMPT and the same rules for its use apply.

TCP_PROMPT

May be set directly. Used as the prefix for data read by tcp_read
which is printed to standard output or to the log file given by
$TCP_LOG, if any. Any `%s', `%f' or `%%'
occurring in the string will be replaced by the name of the session, the
session's underlying file descriptor, or a single `%',
respectively. The expression `%c' expands to 1 if the session being
read is the current session, else 0; this is most useful in ternary
expressions such as `%(c.-.+)' which outputs `+' if the
session is the current one, else `-'.

If the prompt starts with %P, this is stripped and the
complete result of the previous stage is passed through standard prompt
%-style formatting before being output.

TCP_READ_DEBUG

May be set directly. If this has non-zero length, tcp_read will
give some limited diagnostics about data being read.

TCP_SECONDS_START

This value is created and initialised to zero by tcp_open.

The functions tcp_read and tcp_expect use the
shell's SECONDS parameter for their own timing purposes. If that
parameter is not of floating point type on entry to one of the functions, it
will create a local parameter SECONDS which is floating point and set
the parameter TCP_SECONDS_START to the previous value of
$SECONDS. If the parameter is already floating point, it is used
without a local copy being created and TCP_SECONDS_START is not set.
As the global value is zero, the shell elapsed time is guaranteed to be the
sum of $SECONDS and $TCP_SECONDS_START.

This can be avoided by setting SECONDS globally to a
floating point value using `typeset -F SECONDS'; then the TCP
functions will never make a local copy and never set
TCP_SECONDS_START to a non-zero value.

TCP_SESS

May be set directly. The current session; must refer to one of the
sessions established by tcp_open.

TCP_SILENT

May be set directly, although it is also controlled by tcp_log. If
of non-zero length, data read by tcp_read will not be written to
standard output, though may still be written to a log file.

tcp_spam_list

Array. May be set directly. See the description of the function
tcp_spam for how this is used.

TCP_TALK_ESCAPE

May be set directly. See the description of the function tcp_talk
for how this is used.

TCP_TIMEOUT

May be set directly. Currently this is only used by the function
tcp_command, see above.

The following parameters are not set by the function system, but have a special
effect if set by the user.

tcp_on_read

This should be an associative array; if it is not, the behaviour is
undefined. Each key is the name of a shell function or other command, and
the corresponding value is a shell pattern (using EXTENDED_GLOB).
Every line read from a TCP session directly or indirectly using
tcp_read (which includes lines read by tcp_expect) is
compared against the pattern. If the line matches, the command given in
the key is called with two arguments: the name of the session from which
the line was read, and the line itself.

If any function called to handle a line returns a non-zero status,
the line is not output. Thus a tcp_on_read handler containing only
the instruction `return 1' can be used to suppress output of
particular lines (see, however, tcp_filter above). However, the line
is still stored in TCP_LINE and tcp_lines; this occurs after
all tcp_on_read processing.